A tilt rotor aircraft is an aircraft having advantages such as high speed forward flight and long endurance as compared to a general vertical take-off and landing aircraft such as a helicopter, simultaneously with having a vertical take-off and landing function.
A general tilt rotor aircraft includes rotating rotors provided at each of left and right distal ends of a wing and has a structure in which a left rotor and a right rotor rotate in different directions (forward rotate and reversely rotate).
The tilt rotor aircraft may change an angle of a nacelle in which the rotors are mounted according to a flight mode. For example, the tilt rotor aircraft may change the angle of the nacelle so as to be 90 degrees at the time of take-off and landing and to be horizontal to a flight direction, that is, 0 degree, like a fixed wing aircraft at the time of forward flight.
Therefore, the tilt rotor aircraft has both of the advantages such as vertical take-off and landing and high speed forward flight.
In the tilt rotor aircraft, the rotor in the fixed wing flight mode serves to provide thrust for the forward flight and to control yaw movement flight attitude using a difference in thrust between the left rotor and the right rotor.
In addition, a flaperon and an elevator control roll and pitch attitudes (in the case of the tilt rotor aircraft, since a flap is mounted at a tailing edge portion of a main wing and performs both of a flap function for increasing lift in a low speed and an aileron function for controlling a roll attitude, a part performing a flap function and an aileron function will be referred to as the “flaperon”).
In the case of the tilt rotor aircraft, in a hovering mode and a low speed rotary-wing flight mode, the rotor provides the lift and most flight attitude control force.
Further, in transition mode flight, control authorities of the rotor, the flaperon, and the elevator are mixed with each other to form a flight attitude (“transition flight” indicates a process of changing a rotary-wing flight mode into a fixed wing flight mode).
In addition, in the rotary-wing flight mode and a low speed transition flight mode, a tilt angle of the nacelle is almost vertical to a chord direction (meaning a direction indicated by a straight line connecting a lead edge portion and a tailing edge portion of the main wing to each other) of the main wing, and propeller wash of the rotor strikes the main wing, such that download acts on the main wing, thereby generating loss of vertical take-off and landing performance.
In order to minimize this download and maximize the lift of the wing at the time of low speed flight, in the hovering mode and the low speed rotary-wing flight mode, a main wing flaperon angle is increased, and as the nacelle angle is changed from the vertical to the horizontal, the flaperon angle is decreased.
Meanwhile, in a flaperon operator, large operation load capability capable of overcoming a moment generated due to aerodynamic load as well a rapid driving speed for controlling a roll movement attitude in accordance with an increase in a forward flight speed are required.
On the other hand, in the case of a nacelle tilt operator, an operator having a low driving speed and large operation load capability is required.
Further, in the hovering mode and the low speed rotary-wing flight mode, the roll movement attitude control is performed using a difference in a collective pitch angle between the left and right rotors. However, in a process of performing the transition flight, as a flight speed increases, roll movement attitude control capability is insufficient only with the difference in a pitch angle between the left and right rotors, such that the control authorities of the rotor and the flaperon are mixed with each other as described above, thereby forming a flight attitude.
In the tilt rotor aircraft, an aspect ratio of the main wing is relatively smaller than that of the general fixed wing aircraft, and a driving axis connecting a main gearbox and a rotor gearbox to each other passes through an inner portion of the main wing, such that a thickness ratio of an airfoil of the main wing is relatively large. Therefore, performances such as an endurance time and a flight distance are slightly lowered.
In order to supplement these disadvantages, a tilt rotor aircraft in which auxiliary wings having various shapes are mounted outside the nacelle has been suggested in Korean Patent No. 10-0822366.
In the related art as described above, a technology of rotating at the same angle as a nacelle angle by fixing the auxiliary wing to the nacelle has been suggested.
In addition, a concept of allowing rotation of the auxiliary wing, extension of a length of the auxiliary wing, spreading of the auxiliary wing, and the like, to be performed by a separate driving unit has been suggested.
However, a specific unit for separately moving the auxiliary wing has not been suggested, and an auxiliary wing driving unit is used only to minimize the download in the transition flight mode.
However, in the case in which the auxiliary wing is fixed to the nacelle, an angle of attack of the auxiliary wing is significantly increased in a low speed section of the transition flight, such that large drag acts on the auxiliary wing. In addition, in the case in which the auxiliary wing is moved using a separate driving unit, several problems such as an increase in weight, an increase in power consumption, an increase in an electric wiring, complexity of a control logic, and the like, due to mounting of the separate driving unit have been generated.